There are many good reasons for building a web page but it is important that your goals are clear. Your objectives should drive the content and the design of your site. Many people build home pages as a hobby, purely for their own personal development. Others build them to promote business, social, cultural, humanitarian, or business objectives.
Knowledge of web page development can help you in your career. Many businesses today have their own corporate Intranet sites, which are simply internal Internet systems used to share corporate information. The ability to communicate electronically is a valuable skill to employers.
There is also potential for generating income from the web pages you develop. This is done by publishing interesting pages that attract large numbers of visitors and then selling advertising space, goods or services from those pages.
Judging by the vast number of home pages that contain little more than the builder's name, age, and a photograph of the family cat, it would appear that many web page developers have not clearly defined their objectives!